Why use encryption?
Every message transferred via the Internet or related networks passes a number of nodes whose administration and security policies are unknown. Apart from that there is a new technical standard that regulates the so-called lawful interception of communication channels. In order to get your data unharmed and unread through untrusted networks you need to use encryption. Using encryption doesn't mean that you have something to hide, it merely assures that three basic principles of communication are maintained.
Considered the fact that forged messages can be generated by virus/trojan programs or spam sources one can quickly recognize the importance of these three properties. The GNU Privacy Guard (GnuPG) is one of the many means to improve your communication habits. An overview and a little step by step introduction can be found in GnuPG's documentation section.